It was considered that double-blind crossover studies of therapeutic efficacy after acute injury could well be done in patients who required surgical removal of impacted wisdom teeth from both sides of the lower jaw. In the present trial 24 healthy patients received either placebo or ibuprofen (Brufen: 400 mg three times daily), a non-steroidal anti-inflammatory agent, for 5 days commencing the day before surgery. Treatments were given on the two occasions when impacted wisdom teeth were to be removed from one side or other of the lower jaw. A number of objective and subjective parameters were recorded for paired comparison of the post-operative courses, including swelling, trismus and pain. A mechanical device which allows simple and accurate measurement of cheek swelling is described. On the 1st, 3rd and 5th post-operative days in the ibuprofen group the measured swelling averaged 93, 89 and 82%, respectively, of that in the placebo group; the corresponding alpha-values were 0.35, 0.06 and 0.07. Patients with less swelling after ibuprofen were not always those with a high serum concentration of the drug. Ibuprofen significantly reduced pain on the day of the operation. This may at least partly account for less trismus and the preference of the patients for their post-operative courses with ibuprofen. Examination of various haematological parameters did not reveal any significant difference between the two operations. Subjective scores indicated that neither wound-healing nor bleeding was affected by ibuprofen, nor were any side effects detected.